1. Field of the Invention
The present invention relates to the manufacture of honeycomb bodies, and more specifically to a method of producing a honeycomb body comprising metal sheets which are stacked and/or wound in a layer configuration.
2. Description of the Related Art
Honeycomb bodies are used in particular as catalyst carrier bodies for the conversion of exhaust gases of internal combustion engines. Such honeycomb bodies are known for example from international publication WO 89/07488. Catalyst carrier bodies of this type are exposed to high levels of mechanical and thermal loading. Besides the thermal and mechanical loading of the honeycomb body it is exposed to the aggressive gas components which are present in the exhaust gas. The aggressive gas components can result in corrosion of the honeycomb body. It is therefore desirable to produce honeycomb bodies from metal sheets which are resistant to corrosion.
It has become known from European patent EP 0 159 468 B1 to produce honeycomb bodies from steel sheets with a high aluminum content. The production of a honeycomb body from such materials, however, gives rise to problems and involves high costs due to the poor rollability of steel with a high proportion of aluminum.
U.S. Pat. No. 5,366,139 proposes a metal sheet for the production of a honeycomb body which comprises an aluminum-plated steel. The processing of such sheets in the production of the honeycomb body is less expensive as such sheets can be more easily subjected to cold working.
After aluminum-plated metal sheets have been stacked and/or wound in a layered configuration, they are subjected to a subsequent heat treatment. The heat treatment provides for substantial homogenization of metal sheets which have at least a layer of chromium-bearing steel and at least one primarily aluminum-bearing layer. It has been found that, in the production of honeycomb bodies, in particular those with a relatively large cross-section, which have metal sheets with a laminate structure, it is not always possible to guarantee that the metal sheets are connected together and/or to a casing which encloses the honeycomb body. However, a sound connection of the sheet metal layers to each other and/or to a tubular casing enclosing the honeycomb body is a matter of great significance in terms of the mechanical strength of the honeycomb body. It is now known that, when the honeycomb body is subjected to a heat treatment, there may be a reduction in the volume of the sheet metal layers of laminate structure. The reduction in volume of the sheets of a laminate structure is attributed to the fact that the aluminum which forms an outer layer of the metal sheet diffuses into the first layer of chromium-bearing steel, during a heat treatment. The aluminum which diffuses into the layer of chromium-bearing steel however does not increase the volume of that layer, to the extent to which there is the reduction in volume of the aluminum layer. In addition, layered or laminate sheets have only a low degree of elasticity during the homogenization procedure.